There are a number of devices in which a small scale energy production is needed because it may be impossible or at least very difficult to provide energy sources like batteries for such devices. Some non-limiting examples of such devices are tyres comprising a sensor for measuring or sensing some properties of the tyre, for example the air pressure, temperature etc., product sensors attached to a package of the product, for example for producing indication on the conditions by which the product has been affected during transportation and/or storage.
Such sensors are often implemented using short range wireless communication technology i.e. the sensors transmit information by using e.g. radio waves. These kind of sensors are generally called as RFID sensors (Radio Frequency Identification). The RFID sensors need electric energy when information is transmitted to or received from a reader device. In some implementations the energy needed in the RFID sensor is produced by the reader device in the form of an electromagnetic field. However, the distance between the reader device and the RFID sensor should be kept rather small and the energy available at the RFID sensor is very small thus making the RFID technology of prior art not applicable to all applications.
Some efforts have been made to produce electric energy for a device by using a piezo generator. A piezo generator is a device which converts mechanical energy to electric energy using a piezoelectric transducer such as piezoelectric film. However, the energy level produced by such a piezo generator has been quite low for some applications utilising the RFID sensors.